1. Field of the Invention
The invention relates to a vehicle seat apparatus that includes a seat portion and a seatback.
2. Description of Related Art
Published Japanese Translation of PCT application No. 2003-516267 (JP 2003-516267 A) describes a related vehicle seat apparatus. The technology described in JP 2003-516267 A is such that a frame structure of a vehicle seat is able to be adjusted in a spherical manner within two planes that are isolated from each other, by a lift element.
However, the technology described in JP 2003-516267 A only considers a lateral load that acts on an occupant when driving around a curve. Also, with the technology described in JP 2003-516267 A, the lift element is driven by a drive motor, so the vehicle seat is unable to be moved in line with the intentions of the occupant. Therefore, there is room for improvement in terms of improving steering operability and the ability to maintain a posture of the occupant when turning, and the like.
Thus, the applicant of this specification has proposed a vehicle seat apparatus capable of making it easier for an occupant to maintain a posture when turning, in PTC application (PCT/JP2011/068326) filed earlier.
That is, it is known that most movement of a person can be performed more easily and efficiently by starting at the lumbar region (i.e., the lower back), and moving the lumbar region in various directions. For example, with running, a person is able to easily run fast by bending and rotating the lumbar region, and moving the pelvis and the scapula (shoulder blades) in opposite directions. Also, for example, in karate as well, a punch can be delivered with speed and power by bending and twisting the lumbar region, and moving the pelvis and the scapula in opposite directions.
However, a driver is seated in a seat that is fixed to a vehicle, so the lumbar region is fixed. Therefore, the driver must perform driving operations with his or her lumbar region, which is the starting point for natural movement, fixed.
For example, when performing a steering operation, the driver is unable to move the pelvis and the scapula in opposite directions with the lumbar region as the starting point, so the steering wheel must be turned using only the strength of the arms. However, arm muscles have less stamina than the trunk muscles of the lumbar region, so when turning the steering wheel using only the strength of the arms, the arms will easily become fatigued. Moreover, unlike natural movement that starts at the lumbar region, the arms are moved in an unnatural posture in which the lumbar region is fixed, so the shoulders and neck will also easily become fatigued.
Further, the trunk muscles are unable to be used effectively (i.e., unable to generate much power) when the lumbar region is fixed, so lateral rigidity becomes extremely low. Therefore, the driver is forced to rely on side supports of the seat to withstand lateral force acting toward the outside in the direction in which the vehicle is turning, which leads to an increase in weight and size of the seat.
Also, when the lumbar region continues to be fixed for extended periods of time, the trunk muscles of the lumbar region become extremely weak, which leads to back pain. The three major diseases of taxi drivers are lower back pain, hemorrhoids, and gastric ulcers (stomach ulcers), but the cause of these is said to be muscular weakness of the trunk muscles due to driving a vehicle for extended periods of time.
Given this situation, in PCT application (PCT/JP2011/068326) filed earlier, this issue is resolved by making the seat portion of the vehicle seat apparatus movable.
However, when the seat portion of the vehicle seat apparatus is made movable, the posture of the occupant during a turn is able to be easily maintained, but after the turn is finished, the seat portion that has moved may not return to the original position, so the posture of the occupant may not return to the original state.